1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device.
2. Description of the Related Art
In a semiconductor manufacturing step, there is required a technique of forming an opening (for example, an opening for a contact plug) in an insulating member such as an interlayer dielectric film and simultaneously forming another opening having a larger width (size) and a smaller depth than the opening. For example, an alignment mark, a guard ring, or the like can be formed by forming a metal member in the other opening. In a solid-state image sensor including a photoelectric conversion portion, for example, a light-shielding member can be formed at a position close to the upper surface of the semiconductor substrate by forming a metal member in the other opening.
When forming a plurality of openings, whose widths are different from each other, in an insulating member by dry etching, the etching amount per unit time and unit area, that is the etching rate, of the insulating member may be larger in an opening with a larger width than in an opening with a smaller width depending on the etching condition (microloading phenomenon). Depending on another etching condition, the etching amount per unit time and unit area, that is the etching rate, of the insulating member may be larger in an opening with a smaller width than in an opening with a larger width (reverse microloading phenomenon). For this reason, it is not easy to form a plurality of openings, whose widths are different from each other, in an insulating member in consideration of their depths.
Japanese Patent Laid-Open No. 2010-287823 discloses a technique of forming a plurality of openings, whose depths are equal to each other and whose widths are different from each other, using etching with the microloading phenomenon and etching with the reverse microloading phenomenon.
The present inventor attempted to form an opening for a contact plug in an insulating member and simultaneously form an opening for an alignment mark (another opening having a larger width and a smaller depth than the opening for a contact plug) using the above-described two types of etching. A structure serving as the underlying material of the insulating member generally has unevenness (height difference) on the upper surface because of, for example, the gate electrode of a transistor formed on the semiconductor substrate. In this case, the insulating member includes portions whose thicknesses are different from each other. More specifically, the portion on a convex portion of the structure out of the insulating member has a thickness smaller than that of the portion on a concave portion of the structure. For this reason, when forming an opening for a contact plug on each of the convex and concave portions of the structure, the convex portion of the structure is exposed first. The convex portion of the structure may be damaged largely until the concave portion of the structure is exposed.